Electro-chemical machining system



July 24, 1962 R. c. JOHNSON ET AL 3,046,206

ELECTED-CHEMICAL. MACHINING SYSTEM Filed Feb. 25, 1955 INVENTORS SAWYER nite States 3,046,206 Patented July 24, 1962 3 046 206 ELECTROCHEMICAL MACHINING SYSTEM Richard C. Johnson, 11713 Lytle St, Silver Spring, Md., and John W. Sawyer, 4519 18th St., North Arlington,

Filed Feb. 23, 1955, Ser. No. 490,158

Claim. cl. 204-14s) (Granted under Title 35, US. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States ment of any royalties thereon or therefor.

This invention relates generally to a method and an characteristics of the teeth.

Grinding with an abrasive wheel typically produces very fine surface scratches, each of which may constitute and for electrolysis process operates as readily with hard steels as with soft steels.

In addition, electrolysis, automatically, the high points on a metal surface are attacked selectively because of greater current distribution or shorter interelectrode distance that exists between these high points and the cathode. The most highly stressed areas are also attacked selectively because they are anodic rather than adjacent areas of the metal surface. Electrolysis, therefore, is a natural means of leveling a surface, rounding edges, and relieving a relatively stressed area.

In addition to these characteristics, there is another which is of value. That is the absence of heat. At no time during metal removal as here taught, is there any noticeable temperature rise, either of the work or the electrolyte. Thus, there is inherent in the electrochemical method the action of forces working in jected to high compressive stresses, and thermal effects leading to microscopic cracks. The causes of bending, pitting, and scoring failures of gears will therefore be substantially reduced by the electrochemical approach.

determined configuration.

Another object is to shape a member into a predetermined form by electrochemical means.

A still further object is to provide a metal surface that is uniform and free from stressed areas.

Yet another object is to improve on the metal working systems now in us Other objects and many of the attendant advantages of th' readily appreciaed as the same numerals designate like thereof and wherein:

FIG. 1 is a schematic representation of the electrochemical machining system to be hereinafter described;

FIG. 2 is an elevation showing a gear member being formed;

FIG. 3 is an elevation showing another species of tool used for forming gears;

FIG. 4 is an elevation in section of the structure of FIG. 3 turned through degrees; and

1G. 5 is a longitudinal elevation in section showing a cutting tool.

Referring now to the drawings wherein like reference characters designate like or corresponding parts throughviews there is shown in FIG. 1 a variable 10 having terminals to 12 are connected. The

positive lead or anode 12. An element 14 disposed ad- 13 is supported tion with respect thereto and is connected to the negative pump 18 discharges the electrolyte through spray the areas of contact between member ment 13.

When the circuit ment 14 is moved figuration may be realized.

In practicing the above method the best results are ob- 'In general the lower the current density tained in the current density range from 100 amperes to 600 amperes per square inch. If rapid metal removal is desired current densities as high as 1040 amperes per square inch have been found to produce deep etching. the longer is required to remove a given quantity of metal, and the more uniform the final surface.

The relative speed between the moving bodies is preferably maintained between 4700 to 5200 linear feet per minute for best results.

The electrolyte used in the electrochemical machining process offers an additional variable. It has been found that certain electrolytes which permit high metal removal rates result in deep etching action particularly on soft metals. Other selected electrolytes are slower in metal removal rates but provide a more uniform final surface. The following electrolytes, having the slow working characteristics referred to above, are cited by way of example; NaNO plus 1% NaNO and 5% NaNO plus 5% Na S O All electrolytes should be inhibited to protect the work and tools against corrosion, as for example, an oil-in-water emulsion containing about 1% of an emulsifiable naphthenic oil. Sodium silicate solutions have been used and are satisfactory except for the formation of glassy deposits upon drying. As a specific exam- .ple of the results obtained a finish of 7 to 9 microinches- R.M.S. was obtained on tool steel having a hardness of Rockwell C60.

In the description of FIG. 1 above, no mention was made of the engagement between the relatively moving members. The several parts however are in contact, one with another and extreme care must be exercised in the control of this factor to prevent mechanical abrasions removing more metal than is removed by the electrochemical action. If a conforming negatively connected element, or cathode, is not used then line contact may result with the positively connected work, or anode. Line contact introduces difiiculty in the control of pressure of the cathode on the anode and control of current density.

Due to line contact, pressures can be extremely high and if not carefully regulated mechanical abrasion may become excessive and a series of fine surface scratches may result. FIG. 2 illustrates a conforming cathode. t

In FIG. 2 the positive lead 12 is connected through slip rings (not shown) to the work or anode 13. The negative lead 11 connects to cathode 2.0 and pipe 19 is depended upon to furnish an electrolyte to the intergag ing surfaces. Metal is removed fromth e anode by electrochemical action, as previously discussed, and the cathode is shaped to conform to the final configuration of the gear teeth substantially as shown. Thu at the start of the metal removing process the contact may be of somewhat limited area and mechanical abrasion and electrolytic erosion may result, however, this is not deemed material until the final configuration is approached whereupon the area of contact greatly increases, substantially as shown, and an extremely uniform final surface is obtained. FIGS. 3 and 4 taken together show respective views of .a worm hob 21 used to generate cooperating teeth in wormwheel 22. As in above discussed variants the work is connected to the positive terminal of a source of direct current energy and the hob is connected to the negative terminal thereof. Nozzles 19 continuously supply electrolyte to the interengaging metal surfaces and upon moving the members relative one to another metal will be removed from the anode connected member to thereby form it into a predetermined shape.

FIG. 5 illustrates a type of tool which has been successfully used in this novel metal working system. Reference character 24 indicates a shaft adapted to be rotatably supported by bearings 25. The tool 26 is fixedly held for rotation with the shaft by a nut 27 and has in the surface thereof a plurality of imbedded diamonds 28. The tool thus described lends itself to fine pressure and spacing control. If the tool is too close to the work the diamonds tend to cut away the metal in the well known way, however, the diamonds act as insulators to preserve the electrolytic gap. It has also been found that when using an electrolyte that does not remove all phases of the metal at the same rate the diamonds will function mechanically and remove parts of the surface that have been ignored by the action of the electrolysis. It has also been found that the diamonds act to mechanically remove deposits formed on the work surface by action of the electrolyte.

The method thus illustrated may easily and quickly be adapted for use in lapping operations w 'ch may be carried out using the electrolytic-mechanical system instead of lapping compounds between the tooth contact areas on the gear and cast iron lap.

A narrow face lap that will mesh with the gear and at the same time make axial traverses may be used to obtain reduced metal volume on tooth edges or tooth barreling. During the traverse the current is varied with current being a minimum midpoint of the tooth and a maximum at the ends whereby more metal is removal from the ends. Any well known either automatic or manual current control device may beused in this system.

The disclosed-method is also applicable to the wearing in of mating sets of gears. If the pair of gears be connected respectively to the negative and positive terminals of a source of energy and then run in meshing condition with an electrolyte sprayed on the areas of engagement a perfectly matched set is obtained in a time interval that is sharply reduced from the conventional mechanical running.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

r The method of electrochemically lapping a gear which comprises the steps of interconnecting the gear to the positive terminal of a direct current source of electrical energy, interconnecting a lap element to the negative terminal of the source of energy, translating and rotating the gear and lap element relative toeach other, applying an electrolyte between tooth contact areas on the gear andlap element during relative movement thereof, and varying the current applied to the gear and lap element during relative movement thereof in a manner that a minimum current is applied when the lap is at a midpoint of a gear tooth and a maximum at the ends whereby more metal is removed from the ends of the tooth.

References Cited in the file of this patent UNITED STATES PATENTS France Apr. 21, 1954 OTHER REFERENCES Steel, vol. 130, No. 3, Mar. 17, 1952, page 84-86 cited.

when the lap is at the 

